erc-c/src/apple2/apple2.c

/*
 * apple2.c
 *
 * This file handles the top-level domain code for the Apple II machine.
 * It's also a bit of a catch-all for logic which doesn't need its own
 * file.
 */

#include <unistd.h>

#include "apple2/apple2.h"
#include "apple2/debug.h"
#include "apple2/draw.h"
#include "apple2/mem.h"
#include "mos6502/dis.h"
#include "mos6502/enums.h"
#include "objstore.h"
#include "option.h"
#include "vm_di.h"
#include "vm_event.h"
#include "vm_segment.h"

/*
 * This is the memory address where an apple program can find the value
 * of the key that was last pressed.
 */
#define LAST_KEY 0xC000

/*
 * This is the address in memory where you can find whether a key is
 * currently pressed or not.
 */
#define ANY_KEY_DOWN 0xC010

/*
 * Create the basic apple2 structure.
 */
apple2 *
apple2_create(int width, int height)
{
    apple2 *mach;
    int err;

    objstore_init();

    mach = malloc(sizeof(apple2));
    if (mach == NULL) {
        return NULL;
    }

    // By default, we have no strobe set; it should only be set when a
    // key is pressed
    mach->strobe = false;

    // Yes, please do execute opcodes to begin with
    mach->paused = false;

    // Don't print opcodes by default
    mach->disasm = false;

    // Forward set these to NULL in case we fail to build the machine
    // properly; that way, we won't try to free garbage data
    mach->rom = NULL;
    mach->cpu = NULL;
    mach->aux = NULL;
    mach->main = NULL;
    mach->sysfont = NULL;
    mach->invfont = NULL;
    mach->screen = NULL;
    mach->drive1 = NULL;
    mach->drive2 = NULL;
    mach->selected_drive = NULL;

    // This is more-or-less the same setup you do in apple2_reset(). We
    // need to hard-set these values because apple2_set_bank_switch
    // assumes that the bank_switch variable has been initialized
    // before, which to this point, it hasn't!
    mach->bank_switch = BANK_DEFAULT;
    mach->memory_mode = MEMORY_DEFAULT | MEMORY_SLOTCXROM;

    mach->main = vm_segment_create(APPLE2_MEMORY_SIZE);
    if (mach->main == NULL) {
        log_crit("Could not initialize main RAM!");
        apple2_free(mach);
        return NULL;
    }

    mach->cpu = mos6502_create(mach->main, mach->main);
    if (mach->cpu == NULL) {
        log_crit("Could not create CPU!");
        apple2_free(mach);
        return NULL;
    }

    // Initliaze our system ROM and separate bank-switched block of RAM
    mach->rom = vm_segment_create(APPLE2_ROM_SIZE);
    mach->aux = vm_segment_create(APPLE2_MEMORY_SIZE);
    if (mach->rom == NULL || mach->aux == NULL) {
        log_crit("Could not initialize ROM / AUX!");
        apple2_free(mach);
        return NULL;
    }

    // Set the read/write mappers for everything
    apple2_mem_map(mach, mach->main);
    apple2_mem_map(mach, mach->aux);

    if (apple2_mem_init_sys_rom(mach) != OK) {
        log_crit("Could not initialize apple2 ROM");
        apple2_free(mach);
        return NULL;
    }

    // Our two drives -- we create both of them, even if we intend to
    // use only one.
    mach->drive1 = apple2_dd_create();
    mach->drive2 = apple2_dd_create();

    if (mach->drive1 == NULL || mach->drive2 == NULL) {
        log_crit("Could not create disk drives!");
        apple2_free(mach);
        return NULL;
    }

    // By default, the selected drive should be drive1
    mach->selected_drive = mach->drive1;

    // Let's build our screen abstraction!
    mach->screen = vm_screen_create();
    if (mach->screen == NULL) {
        log_crit("Screen creation failed!");
        apple2_free(mach);
        return NULL;
    }

    // We still need to add a window, since we want to render some
    // graphics.
    err = vm_screen_add_window(mach->screen, width, height);
    if (err != OK) {
        log_crit("Window creation failed!");
        apple2_free(mach);
        return NULL;
    }

    // Default to full color
    apple2_set_color(mach, COLOR_FULL);

    // We default to lo-res mode.
    apple2_set_display(mach, DISPLAY_TEXT);

    // Let's install our bitmap font.
    mach->sysfont = vm_bitfont_create(mach->screen,
                                      objstore_apple2_sysfont(),
                                      APPLE2_SYSFONT_SIZE,
                                      7, 8,         // 7 pixels wide, 8 pixels tall
                                      0x7f);        // 7-bit values only
    mach->invfont = vm_bitfont_create(mach->screen,
                                      objstore_apple2_invfont(),
                                      APPLE2_SYSFONT_SIZE,
                                      7, 8,
                                      0x7f);
    if (mach->sysfont == NULL || mach->invfont == NULL) {
        apple2_free(mach);
        log_crit("Could not initialize apple2: bad font");
        return NULL;
    }

    return mach;
}

/*
 * Change the bank switch flags for the apple 2.
 */
void
apple2_set_bank_switch(apple2 *mach, vm_8bit flags)
{
    // If we already have BANK_ALTZP, and the flags we're setting do
    // _not_ have BANK_ALTZP, then we need to copy aux's zero page and
    // stack into main. But if we don't have BANK_ALTZP, and flags
    // _does_, then we have to do the inverse: copy main's zero page and
    // stack into aux. 
    if (mach->bank_switch & BANK_ALTZP) {
        if (~flags & BANK_ALTZP) {
            vm_segment_copy(mach->main, mach->aux, 0, 0, 0x200);
        }
    } else if (flags & BANK_ALTZP) {
        vm_segment_copy(mach->aux, mach->main, 0, 0, 0x200);
    }

    mach->bank_switch = flags;
}

/*
 * Set the memory mode of the apple machine. This may cause us to change
 * some behavior (i.e. start using or stop using auxiliary memory).
 */
void
apple2_set_memory_mode(apple2 *mach, vm_8bit flags)
{
    vm_segment *rmem = NULL, 
               *wmem = NULL;

    mach->memory_mode = flags;

    // We may need to change which segments the CPU can read from or
    // write to, based upon the below flags. 
    rmem = (flags & MEMORY_READ_AUX) ? mach->aux : mach->main;
    wmem = (flags & MEMORY_WRITE_AUX) ? mach->aux : mach->main;

    mos6502_set_memory(mach->cpu, rmem, wmem);
}

/*
 * Return true if we are in a state that the apple2 would consider
 * double resolution. (In practice, this refers to horizontal screen
 * density; vertical screen density per-pixel is unchanged.)
 */
bool
apple2_is_double_video(apple2 *mach)
{
    return 
        mach->display_mode & DISPLAY_DHIRES;
}

/*
 * Try to "boot" the apple2 machine. Look for input sources indicated in
 * the option system and load those into our disk drives.
 *
 * FIXME: we need to get the image type from the file name used
 */
int
apple2_boot(apple2 *mach)
{
    FILE *stream;
    int err;

    // Do we have any disks?
    stream = (FILE *)vm_di_get(VM_DISK1);
    if (stream) {
        err = apple2_dd_insert(mach->drive1, stream, DD_DOS33);
        if (err != OK) {
            log_crit("Unable to insert disk1 into drive");
            return err;
        }
    }

    stream = (FILE *)vm_di_get(VM_DISK2);
    if (stream) {
        err = apple2_dd_insert(mach->drive2, stream, DD_DOS33);
        if (err != OK) {
            log_crit("Unable to insert disk2 into drive");
            return err;
        }
    }

    // To begin with, we need to set the reset vector to the Applesoft
    // interpeter.
    vm_segment_set16(mach->main, APPLE2_RESET_VECTOR,
                     APPLE2_APPLESOFT_MAIN);

    // Run the reset routine to get the machine ready to go.
    apple2_reset(mach);

    return OK;
}

/*
 * This function marks out the procedures that happen when the machine
 * is reset. A reset can happen at a cold boot, but it can also happen
 * after the computer is already operational.
 */
void
apple2_reset(apple2 *mach)
{
    mach->cpu->P = MOS_STATUS_DEFAULT;
    mach->cpu->PC = vm_segment_get16(mach->main, 0xFFFC);
    mach->cpu->S = 0xff;

    // Switch video mode back to 40 column text
    apple2_set_display(mach, DISPLAY_TEXT);

    // Switch us back to defaults
    apple2_set_bank_switch(mach, BANK_DEFAULT);
    apple2_set_memory_mode(mach, MEMORY_DEFAULT | MEMORY_SLOTCXROM);
}

/*
 * Free the memory reserved for an apple2 struct.
 */
void
apple2_free(apple2 *mach)
{
    if (mach->cpu) {
        mos6502_free(mach->cpu);
    }

    if (mach->rom) {
        vm_segment_free(mach->rom);
    }

    if (mach->main) {
        vm_segment_free(mach->main);
    }

    if (mach->aux) {
        vm_segment_free(mach->aux);
    }

    if (mach->sysfont) {
        vm_bitfont_free(mach->sysfont);
    }

    if (mach->drive1) {
        apple2_dd_free(mach->drive1);
    }

    if (mach->drive2) {
        apple2_dd_free(mach->drive2);
    }

    if (mach->screen) {
        vm_screen_free(mach->screen);
    }

    // NOTE: we do _NOT_ want to clear the memory field of mach, as it's
    // co-owned with the cpu struct that we just freed above.

    free(mach);
}

/*
 * The run loop is the function that essentially waits for user input
 * and continues to present the apple2 abstraction for you to use. At
 * some point the user will indicate they are done, whereby
 * vm_screen_active() will no longer be true and we exit.
 */
void
apple2_run_loop(apple2 *mach)
{
    FILE *dlog = (FILE *)vm_di_get(VM_DISASM_LOG);
    int sleep = 5;

    if (dlog != NULL) {
        mach->disasm = true;
    }

    int i = 0;
    while (vm_screen_active(mach->screen)) {
        i++;

        if (i % sleep == 0) {
            usleep(10);
            i = 0;
        }

        if (apple2_debug_broke(mach->cpu->PC)) {
            mach->paused = true;
        }

        // If we're paused, then just re-loop until we're not
        if (mach->paused) {
            if (mach->selected_drive) {
                mach->selected_drive->locked = true;
            }

            mos6502_dis_opcode(mach->cpu, stdout, mach->cpu->PC);

            if (mach->selected_drive) {
                mach->selected_drive->locked = false;
            }

            char *input = apple2_debug_prompt();

            if (input != NULL) {
                apple2_debug_execute(input);
            }

            free(input);
            continue;
        }

        if (mach->disasm) {
            if (mach->selected_drive) {
                mach->selected_drive->locked = true;
            }
            
            mos6502_dis_opcode(mach->cpu, dlog, mach->cpu->PC);

            if (mach->selected_drive) {
                mach->selected_drive->locked = false;
            }
        }

        if (!apple2_debug_broke(mach->cpu->PC)) {
            mos6502_execute(mach->cpu);
        }

        if (vm_screen_dirty(mach->screen)) {
            apple2_draw(mach);
            vm_screen_refresh(mach->screen);
        }
    }
}

/*
 * Set the color mode of the apple2, which is to say if we are emulating
 * a monochromatic display, or full color, or just black-and-white.
 */
void
apple2_set_color(apple2 *mach, int mode)
{
    mach->color_mode = mode;
    
    // FIXME: doing this should force us to redraw everything in the
    // correct color interpretation
}

/*
 * Set the display mode of the display. This would be the type of
 * resolution (text by which number of columns, lo-res, hi-res, etc.)
 */
void
apple2_set_display(apple2 *mach, vm_8bit mode)
{
    int width, height;

    mach->display_mode = mode;

    // In the traditional video modes that Apple II first came in, you
    // would have a maximum width of 280 pixels. (In lo-res, you have
    // fewer pixels, but that is something we have to handle in our
    // drawing functions rather than by changing the logical size.)
    width = 280;
    height = 192;

    // In double video modes, the width is effectively doubled, but the
    // height is untouched.
    if (apple2_is_double_video(mach)) {
        width = 560;
    }

    vm_screen_set_logical_coords(mach->screen, width, height);
}

/*
 * Tell the screen that it has a change ready to be displayed. This
 * function will not immediately redraw the screen, and when the screen
 * is redrawn is up to our framerate cycle.
 */
void
apple2_notify_refresh(apple2 *mach)
{
    if (mach && mach->screen) {
        mach->screen->dirty = true;
    }
}